Download notes on volcanoes File

What determines the
shape of a volcano?
Entry task
Finish
this sentence.
–The Pacific coast is dotted
with volcanoes because
of……
Make two complete
observations and one inference
about what this is a picture of.
Volcanoes
Nature’s pyrotechnics
Causes

Most occur at plate boundaries
– 15% at divergent boundaries
– 80% at subduction
– 5% at hot spots (Hawaii, Yellowstone)
Volcano Distribution
Volcanoes are found along plate boundaries & over mantle
hot spots…
Ring of Fire… Approximately two-thirds of the
active volcanoes are concentrated along the Pacific
Types of eruptions

Nonexplosive
– Calm lava flows, often
through fissures
– Huge amounts of lava
form the Columbia
Plateau in central WA,
Snake River Plain in
southern ID

Lava Plateau: extensive plain
formed when lava oozes from
fissures ~ Columbia Plateau
Types of eruptions

Explosive
– Less common but
most publicized
– Beside lava, clouds of
hot debris, ash, gas
(Mt. St. Helens)
– 100,000X stronger
than an atomic Bomb
Types of Volcanoes
Three types of volcanoes
1. Shield
2. Cinder Cone
3. Composite
Types of Volcanoes
(Structures)

Shield Volcano
– passive eruptions

Cinder Cone
– explosive and passive eruptions

Stratovolcano/Composite
Cone
– explosive
Comparison of Volcanic
Landforms
Shield
Wide, gently sloping
 Nonexplosive
 Mauna Kea, Hawaii

Shield volcano
Mauna Loa, Hawaii
Shield Volcanoes
 Made
of lava flows
 Huge
structure with massive width to
height ratio
 Looks
like a Roman shield lying on
it’s side
Cinder Cone
Smaller, steeper
 Easily eroded
 Loose pyroclastic material
 Moderately explosive
 In clusters
 Paricutin, Mexico

Cinder Cone

Short-lived volcano that shoots “jets” of
lava into air

Particles cool in mid-air and are deposited
on flank of volcano

Commonly associated with larger volcanic
structures
Cinder Cone
Cinder Cone Volcano
Composite volcano
Composite (stratovolcano)
Most common
 Most explosive
 Alternating ash and lava layers
 Gentle base,
steep top


Mt. Rainier, WA
Composite Volcanoes
or
Stratovolcanoes

Steep slopes, cone shape

Usually explosive

Alternating layers of pyroclastic material,
and high-viscosity degassed lava flows
Composite
Volcanoes
Mt. Rainier
Mt. Fuji, Japan
Crater ~ funnel shaped pit
Caldera: Large depression from
collapsed volcano
ex: Crater Lake, OR
Crater Lake
Formed around 7,700 years ago.
 1,949 feet deep
 No incoming or out flowing rivers.
 Stocked with fish from 1888-1941.


All of the water is replaced every 250
years.
What is a Caldera?
Massive explosive eruption causes
COLLAPSE of volcano into magma
chamber
 Up to 60 km across
 Cyclical process

Large caldera eruption could
end human existence!!!
Classes of volcanoes

Active: has had at least one eruption in
the past 10,000 years.

Dormant: has not erupted in the past
10,000 years, but is expected to.

Extinct: no one expects it to erupt again, a
dried up magma chamber.
Eruption from space